Scintillation camera device

ABSTRACT

A scintillation camera device wherein output pulse signals from photomultipliers optically coupled with a scintillator giving forth light upon absorption of radiation from a radioactive isotope taken into a foreground subject are supplied to a delay element such as a delay line for separating said output signals in time sequence so as to render them proportionate to the coordinate position of said photomultipliers; output signals from the delay element are shaped into bipolar symmetrical waves in a double delay line type wave forming circuit in such a manner that the zero-crossing time of a composite of wave forms is obtained in accordance with the co-ordinate position of the scintillation point; and the zero-crossing time of said composite wave form is converted to voltage, which is indicated on a cathode ray tube as the position of the scintillation point.

United States Patent Tanaka et al.

[ 51 Sept. 12, 1972 [54] SCINTILLATION CAMERA DEVICE [72] Inventors:Elichi Tanaka, Tokyo; Toshiyuki Hiramoto; Norimasa Nohara, both ofChiba, all of Japan [73] Assignee: Director National Institute ofRadiological Sciences, Science and Technology Agency, Chiba-shi, Japan[22] Filed: Oct. 1, 1970 [21] Appl. No.: 77,305

[30] Foreign Application Priority Data ZERO cR ss PULSE HEIGHT PrimaryExaminer-James W. Lawrence Assistant Examiner-Davis L. WillisAttorney-Flynn & Frishauf [5 7] ABSTRACT A scintillation camera devicewherein output pulse signals from photomultipliers optically coupledwith a scintillator giving forth light upon absorption of radiation froma radioactive isotope taken into a foreground subject are supplied to adelay element such as a delay line for separating said output signals intime sequence so as to render them proportionate to the co-ordinateposition of said photomultipliers; output signals from the delay elementare shaped into bipolar symmetrical waves in a double delay line typewave forming circuit in such a manner that the zerocrossing time of acomposite of wave forms is obtained in accordance with the co-ordinateposition of the scintillation point; and the zero-crossing time of saidcomposite wave form is converted to voltage, which is indicated on acathode ray tube as the position of the scintillation point.

,5 Claims, 8 Drawing figures PULSE HEIGHT ANALYZER I l l I I l l I I I lI I I l I SCINTILLATION CAMERA DEVICE The present invention relates toimprovements in a scintillation camera device used in nuclear medicineto determine the distribution of a radioactive isotope taken into ahuman body or other objects.

When radiation emitted from a radioactive isotope taken into aforeground subject are conducted to a scintillator through a collimator,said scintillator gives forth fluorescent rays. Since the position ofthe scintillation point corresponds to the position of a radioactiveisotope present in the foreground subject, the plane distribution ofsaid radioactive isotope is observed in the form of an image of lightgiven forth by the scintillator. Since, however, this light is extremelyfaint, there are used, for example, a plurality of photoamplifierscoupled with a scintillator which are arranged in the form of a regularhexagon in order to intensify said light. Outputs from thephotoamplifiers are proportionate to the intensity of light initiallyintroduced into the scintillator. lf, therefore, outputs from those ofthe photomultipliers which are disposed close to the scintillation pointare indicated on a cathode ray tube, then it will be possible todetermine the position of a scintillation point. The prior artscintillation camera, however, which is only provided with a limitednumber of photomultipliers has caused outputs from the photomultipliersto be multiplied by weighting factors specified for saidphotomultipliers using a resistance matrix in order to find the exactposition of the scintillation point. Now with only one dimension takeninto consideration, let one of the longest diagonal lines of a regularhexagon representing the arrangement of photomultipliers be designatedas a coordinate axis X, those of the photomultipliers disposed on saidaxis X as a, b, c, d and e and outputs therefrom as a,, b 0,, a and e,.These outputs a,, b,, c,, d and e are multiplied by two groups ofweighting factors, the weighting factors of one group denoted, forexample, as K,, K K K and K linearly decrease in the order mentioned.The weighting factors of the other group represented, for example, as HH H H and H linearly increase in turn. Let it be assumed that a total ofproducts arrived at by multiplying outputs a,, b,, 0,, a and e from thephotomultipliers by the weighting factors K K K K and K respectively isdesignated as X*. Then there results the equation:

On the other hand, let a total of products obtained by multiplying saidoutputs by H H H H and H respectively be denoted as X. Then thereresults the equation:

The value of X X X is calculated from the above equations to find theposition of the scintillation point on the axis X. Since outputs fromthe photomultipliers are multiplied by the aforementioned weightingfactors using a resistance matrix, the conventional device has thedrawbacks that outputs from those of the photomultipliers which aredisposed remote from the scintillation point are always multiplied by afixed weighting factor, even when there are introduced only smallamounts of light into the scintillator and consequently statisticalfluctuations in the number of photoelectrons brought to the first dynodeof the photomultiplier and noises caused by the scattering of light areunduly emphasized, resulting in the failure to determine the exactposition of a scintillation point and the decreased resolving power ofthe camera device. Further, the limited number of photomultipliers mostlikely causes the optical image of a radioactive isotope taken into aforeground subject to be distorted on the edge. However, there has notheretofore been developed any suitable means conducive to the resolutionof the aforesaid shortcomings encountered with the conventionalscintillation camera device.

SUMMARY OF THE INVENTION -The object of the present invention is toprovide a scintillation camera device wherein output signals from thephotomultipliers are separated in time sequence in accordance with theco-ordinate position of said photomultipliers by using a delay elementsuch as a delay line; outputs from said delay element such as a delayline are shaped into bipolar symmetrical wave forms in a wave formingcircuit comprising a double delay line, thereby detecting the exactposition of a scintillation point utilizing the fact that thezerocrossing time of a composite of said symmetrical wave formscorresponds to the position of the scintillation point.

The present invention enables outputs from those of the photomultiplierswhich are disposed remote from the scintillation point to be excludedfrom the determination of its position, thereby offering a novelscintillation camera device capable of obtaining signals denoting theexact position of the scintillation point and accurately resolving theoptical image of a radioactive isotope taken into a foreground subject.

This invention can be more fully understood from the following detaileddescription when taken in connection with the accompanying drawings, inwhich:

FIG. 1 presents a schematic arrangement of a scintillation camera deviceaccording to an embodiment of the present invention;

FIG. 2 is a sectional view on line 11 II of FIG. 1;

FIG. 3 is a concrete circuit diagram of a wave forming circuit used inFIG. 1;

FIG. 4A shows output pulses from the photomultipliers with respect tothe scintillation point of FIG. 1;

FIG. 4B indicates the wave forms of outputs from the delay line of FIG.1;

FIG. 4C illustrates the shaped wave forms of FIG. 4B;

FIG. 4D presents a composite pattern of the wave forms of FIG. 4C; and

FIG. 5 is a block circuit diagram of a scintillation camera deviceaccording to another embodiment of the invention.

As shown in FIG. 1, there are positioned above a foreground subject 1 ascintillator 2 for giving forth fluorescent rays upon absorption ofradiation emitted from a radioactive isotope taken into the foregroundsubject 1 and a plurality of photomultipliers 4 for detectingfluorescent rays from the scintillator 2 through a light guide 3 andconverting said rays to electrical signals. Said photomultipliers 4comprise nineteen units assembled, for example, in the form of asubstantially regular hexagon illustrated in FIG. 2. Some of saidphotomultipliers 4 are linearly arranged on one of the longest diagonallines of the hexagon. The scintillator 2, light guide 3 and pluralphotomultipliers 4 are enveloped in a photomagazine 5 and placed in abox member 6. The lower open part of the box member 6 facing theforeground subject 1 is fitted with a collimator 7 for collimatingradiation emitted from the radioactive isotope taken into the foregroundsubject 1. Output signals from the plural photomultipliers are conductedto the terminals of a delay line '10 through pre-amplifiers 8 andconverters 9. The delay line 10 may be replaced by a delay element. Bothterminals of the delay line are grounded through the respectiveresistors 11. One of said terminals is connected to the input terminalof the wave forming circuit 12, the output terminal of which isconnected to the input terminal of a cathode raytube through a zerocrossing discriminator 13 and a time-to-pulse height converter 14 inturn. The wave forming circuit consists of a double delay line connectedas in FIG. 3.

A circuit 16 extending from the preamplifiers 8 supplied with outputsfrom the photomultipliers 4 to the terminal X of the cathode ray tube isused to determine the position of the co-ordinate axis X included inthose axes which indicate the scintillation point. With respect to theco-ordinate axis Y, there is connected to the terminal Y of the cathoderay tube 15 another circuit 17 of exactly the same arrangement as thecircuit 16. The output terminals of the plural photomultipliers 4 areconnected to a mixer 18, where outputs therefrom are added up. Signalsrepresenting a sum of said outputs are conducted through a pulse heightanalyzer 19 to the time-to-height converter 14, and also to the terminalZ of the cathode ray tube 15 for unblanking.

There will now be described the operation of scintillation camera deviceaccording to an embodiment of the present invention with particularreference for briefness only to one dimension (for example, thecoordinate axis X).

Radiation emitted at point 20 of the foreground subject l is conductedthrough the collimator 7 and absorbed into the scintillator 2, causingit to give forth light. Said light is introduced through the light guide3 into the photomultipliers 4 to be converted to current. Outputs fromthe photomultipliers 4 assume the wave forms of FIG. 4A which areproportionate to the quantity of light brought in. Said outputs areamplified by the preamplifiers 8 and converted to current by theconverter 9 and then supplied to the delay line 10. Outputs from thedelay line 10 are separated, as illustrated in FIG. 4B, in time sequencein accordance with the position of the photomultipliers on theco-ordinate axis X. Outputs thus separated are shaped by the waveforming circuit 12 into bipolar symmetrical wave forms indicated in FIG.4C. A composite of said symmetrical wave forms presents such a form asshown in FIG. 4D. The zero-crossing time of said composite wave formcorresponds to the position of the scintillation point on theco-ordinate axis X shown in FIG. 4A. Signals representing thezero-crossing time are detected by the zero cross discriminator andconverted to voltage by the time-to-pulse height converter 14.

The time-to-pulse height converter 14 generates a voltage proportionateto a balance between the time required for outputs from pulse heightanalyzer 19 to be conducted to said converter and the zero-crossingtime. The output voltage from the time-to-pulse height converter 14 isfed to the cathode ray tube 15 as a signal denoting the position of ascintillation point. The output signal from the pulse height analyzer 19is also conducted to the terminal Z of the cathode ray tube 15 forunblanking.

According to the present invention, outputs from the photomultipliersare shaped into bipolar symmetrical wave forms by a wave forming circuitcomprising a double delay line and the position of a scintillation pointcan be determined from the zero-crossing time of a composite of saidsymmetrical wave forms, thus eliminating the necessity of multiplyingoutputs from the photomultipliers 4 by weighting factors.

FIG. 5 is a block circuit diagram of a scintillation camera deviceaccording to another embodiment of the present invention only associatedwith one dimension (for example, the co-ordinate axis X). In FIG. 5,preamplifiers 8 are connected to the photomultipliers 4. The outputterminals of the pre-amplifiers 8 are connected to the delay line 10through a resistor 23 and the converter 9 for converting voltage tocurrent. There is also provided a variable resistor 24 so as toeliminate peripheral distortions on the edge of an image of theradioactive isotope taken in a foreground subject. Both ends of thedelay line 10 are grounded through the resistor 11. To both outputterminals of the delay line 10 are connected a first and a second seriescircuit, each of which is comprised of the wave forming circuit 12, zerocrossing discriminator l3 and time-to-pulse height converter 14. Outputsconducted from the photomultipliers 4 through the pre-amplifiers 8 andconverters 9 to the delay line 10 are separated, as shown in FIG. 4B, intime sequence in accordance with the position of the photomultipliers 4on the co-ordinate axis X. In the wave forming circuit 12 included inthe first series circuit connected to one end of the delay line 10,outputs from said delay line 10 are shaped into bipolar symmetrical waveforms illustrated in FIG. 4C. The zerocrossing time T of a composite ofsaid symmetrical wave forms corresponds to the position of ascintillation point on the co-ordinate axis X. Signals representing thezero-crossing time T are detected-by the zero crossing discriminator l3,and converted to voltage by the time-to-pulse height converter 14,obtaining signals X denoting the position of a scintillation point intothe positive direction of the co-ordinate axis X. Similarly from thesecond series circuit connected to the other end of the delay line 10are obtained signals X representing the position of a scintillationpoint in the negative direction of the co-ordinate axis X. There is alsoprovided a differential amplifier 22 to determine a balance between thevalues of the signals X and X, thereby obtaining signals X indicatingthe position of a scintillation point on the co-ordinate axis X.

On the other hand, output signals from the photomultipliers 4 added upby the mixer 18 are proportionate to gamma ray energy and are fed to thepulse height converter 14. The time-to-pulse height connector generatesa voltage proportionate to a balance between the required outputs fromthe pulse height analyzer l9 and zero-crossing time. Signals X from thedifferential amplifier 22 which denote the position of a scintillationpoint on the co-ordinate axis X are fed to the cathode ray tube.

As mentioned above, the present invention comprises a delay lineassociated with the co-ordinate axes X and Y and a wave forming circuitcomprising a double delay line to exclude outputs from those of thephotomultipliers 4 which are disposed distant from a scintillation pointin determining its position, thereby providing a scintillation cameradevice having a good resolving power.

What we claim is:

l. A scintillation camera device comprising a scintillator for givingforth light upon absorption of radiation from a radio active isotopetaken into a foreground subject; a plurality of photomultiplierssupplied with light from the scintillator; delay elements correspondingto the co-ordinate axes X and Y respectively for separating outputs fromthe photomultipliers in time sequence in accordance with the co-ordinateposition of said photomultipliers; wave forming circuits associated withthe co-ordinate axes X and Y for shaping outputs from said delayelements into bipolar symmetrical wave forms; zero-crossingdiscriminators associated with the co-ordinate axes X and Y fordetecting the zero-crossing time of a composite to bipolar symmetricalwave forms obtained from the wave forming circuit; time-to-pulse heightconverters associated with the co-ordinate axes X and Y for convertingto voltage the signals representing the zero-crossing time of saidcomposite wave form from the zero cross discriminator and a cathode raytube to which there is connected the output terminal of thetime-to-pulse height converter.

2. A device according to claim 1 wherein said wave forming circuitcomprises a double delay line.

3. A device according to claim 1 wherein there is connected between theoutput terminals of the photomultipliers and delay line a series circuitincluding a pre-amplifier and a converter for converting voltage tocurrent.

4. A scintillation camera device comprising a scintillator for givingforth light upon absorption of radiation emitted from a radioactiveisotope taken into a foreground subject; a plurality of photomultiplierssupplied with light from the scintillator; delay elements for separatingoutputs from the photomultipliers in time sequence in accordance withthe co-ordinate position of said photomultipliers; series circuits eachcomprising a pre-amplifier for conducting outputs from thephotomultipliers to said delay elements and a converter for convertingvoltage to current; first and a second conversion circuits eachcomprised of wave forming circuits connected to both ends of therespective delay elements associated with the co-ordinate axes forshaping outputs from the delay elements into bipolar symmetrical waveforms in order to convert said outputs to signals denoting the positionof a scintillation point, zero crossing discriminators for detecting thezerocrossing time of a composite of said bipolar symmetrical wave formsand time-to-pulse height converters for converting to voltage signalsfrom the zero crossing discriminators representing the zero-crossingtime; a differential amplifier for determining a balance between thevalues of outputs from said time-to-pulse height converters; a cathoderay tube connected to the output terminals of the differential amplifieron each co-ordinate axis; a mixer for adding up outputs from the preamlifiers; and a ulse hei ht anal e r for selectin tho e of the outpu fromth% mixer xvfiuch are propor tionate to gamma ray energy and supplyingthe selected outputs to the time-to-pulse height converter.

5. A device according to claim 4 comprising a connecting component whichincludes a converter and a variable resistor for eliminating peripheraldistortions associated with the outermost of the photomultipliers.

1. A scintillation camera device comprising a scintillator for givingforth light upon absorption of radIation from a radio active isotopetaken into a foreground subject; a plurality of photomultiplierssupplied with light from the scintillator; delay elements correspondingto the co-ordinate axes X and Y respectively for separating outputs fromthe photomultipliers in time sequence in accordance with the co-ordinateposition of said photomultipliers; wave forming circuits associated withthe coordinate axes X and Y for shaping outputs from said delay elementsinto bipolar symmetrical wave forms; zero-crossing discriminatorsassociated with the co-ordinate axes X and Y for detecting thezero-crossing time of a composite to bipolar symmetrical wave formsobtained from the wave forming circuit; time-to-pulse height convertersassociated with the co-ordinate axes X and Y for converting to voltagethe signals representing the zero-crossing time of said composite waveform from the zero cross discriminator and a cathode ray tube to whichthere is connected the output terminal of the time-to-pulse heightconverter.
 2. A device according to claim 1 wherein said wave formingcircuit comprises a double delay line.
 3. A device according to claim 1wherein there is connected between the output terminals of thephotomultipliers and delay line a series circuit including apre-amplifier and a converter for converting voltage to current.
 4. Ascintillation camera device comprising a scintillator for giving forthlight upon absorption of radiation emitted from a radioactive isotopetaken into a foreground subject; a plurality of photomultiplierssupplied with light from the scintillator; delay elements for separatingoutputs from the photomultipliers in time sequence in accordance withthe co-ordinate position of said photomultipliers; series circuits eachcomprising a pre-amplifier for conducting outputs from thephotomultipliers to said delay elements and a converter for convertingvoltage to current; first and a second conversion circuits eachcomprised of wave forming circuits connected to both ends of therespective delay elements associated with the co-ordinate axes forshaping outputs from the delay elements into bipolar symmetrical waveforms in order to convert said outputs to signals denoting the positionof a scintillation point, zero crossing discriminators for detecting thezero-crossing time of a composite of said bipolar symmetrical wave formsand time-to-pulse height converters for converting to voltage signalsfrom the zero crossing discriminators representing the zero-crossingtime; a differential amplifier for determining a balance between thevalues of outputs from said time-to-pulse height converters; a cathoderay tube connected to the output terminals of the differential amplifieron each co-ordinate axis; a mixer for adding up outputs from thepre-amplifiers; and a pulse height analyzer for selecting those of theoutputs from the mixer which are proportionate to gamma ray energy andsupplying the selected outputs to the time-to-pulse height converter. 5.A device according to claim 4 comprising a connecting component whichincludes a converter and a variable resistor for eliminating peripheraldistortions associated with the outermost of the photomultipliers.